Well, the only things I can think of would be a potentially different angle (depends how you do them of course), and therefore slightly different muscle emphasis, and relative to pullups, rack chins put you at a mechanical advantage overall, so a person logically should be able to do more and/or heavier reps. Simliar to chinups being mechanically advantageous relative to pullups, only more so.
Personally, I think all these things are good. Weighted, unweighted, whatever angles and grips. Actually, inverted rows are also good - throw on a good weight vest, and they're suddenly not so "easy" after all.
Why not do both, IMO. For the record, I don't, but mostly because it's tricky getting hold of a (okay, THE) rack at the best of times as it is, lol.
Last edited by Dray; 06-11-2013 at 01:02 PM.